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The challenge of solar rechargeable batteries
- Jun 25, 2018 -

1 Energy density

Conventional lithium-ion batteries often use a roll-type packaging method to increase their energy density, but it is not feasible for a "solar battery-energy storage battery" integrated system. Because the lithium-ion battery's packaging affects the area that receives solar energy. The number and power of solar cells need to be matched with the energy storage section to solve the available PV surface area, the number of possible stacked cells and the power matching requirements. The use of high specific-capacity materials as electrodes can increase the overall energy density of the system. For example, silicon-NMC batteries have an energy density of 400 kW/kg, and silicon is a photovoltaic material if silicon can be used as a lithium ion in an integrated system. The electrodes can also be used as photovoltaic electrodes, which will be an ideal design. Silicon solar cells require a high degree of crystallinity, and the insertion of lithium will reduce the crystallinity of silicon, which requires finding an optimal balance point. The study of lithium metal batteries also offers the possibility to increase the overall energy density of the system. In addition, it has been reported in the literature that the photoconversion material perovskite has been shown to have the ability to intercalate lithium ions, and that doping lithium ions in perovskites has a positive influence on its photovoltaic performance, which makes it possible for perovskites to become integrated photovoltaic cells. System high-capacity dual-function material. For applications that require higher volumetric energy, it will be more appropriate.

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2 Overall efficiency

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Figure 2 Efficiency of integrated solar cell-energy storage cell systems in recent years

The overall efficiency of the idealized integrated system is the product of the solar energy conversion efficiency and the energy storage system. The maximum efficiency that the integrated system can achieve is limited by the solar energy conversion efficiency. In reality, the efficiency of the integrated system in the design must also take into account various losses. Silicon solar cells and perovskite batteries can provide more efficient photoelectric conversion and provide better overall efficiency in integrated systems. Another factor to consider if the solar cell is to provide greater efficiency is Maximum Power Tracking (MPPT), which allows the solar cell to provide maximum power. For energy storage batteries, the most suitable positive and negative electrodes need to be selected to maximize Coulomb efficiency.

3 Stability

Stability needs to consider light stability, electrochemical stability, and environmental stability, which requires careful selection of electrode materials. Although people have made gratifying progress in the study of the stability of perovskite solar cells, they are still at a preliminary stage of research. If perovskite is selected as the photovoltaic part of the integrated system, there is a need for greater research on perovskites. Break through. The use of liquid electrolyte is also not conducive to the stability of the system, you can choose to use solid electrolyte to improve the overall system safety and stability. Because the solar cell part will generate heat, the high temperature performance of the energy storage cell electrode material must be considered at the same time.

The integrated "solar battery-energy storage battery" system is still in the early stage of research and development. The literature reports so far have focused on the feasibility of innovative material development and new equipment designs. Future research should continue to develop in this direction. The novel design needs to be combined with high capacity, high efficiency and more stable materials. Optimization of the integrated system can use the following strategies, such as the use of energy conversion and storage of dual-function materials, the use of large-capacity energy storage materials, maximum power tracking, integrated lithium-ion capacitors, use of solid-state electrolytes, improved compatibility between electrochemical electrodes and electrolytes, etc. . Integrated systems can use simulation or modeling methods to better predict system performance and provide better design solutions for integrated systems. In addition, future efforts should combine the integration of "solar battery-energy storage battery" systems with practical applications such as sensor networks, wearables, and electronic devices. Although the current commercialization of "solar battery-energy storage battery" integrated system still has a long way to go, its development will greatly benefit from the current rapid progress in the field of photovoltaic and battery. Its future development will also be directed toward low-power, compact applications, and then to large-scale energy applications.